The eye is fundamentally one of the most important organs during life. Because of aging, diseases and other factors which can adversely affect vision, the ability to maintain the health of the eye becomes all important. The leading cause of blindness is the inability in the treatment of eye diseases to introduce drugs or therapeutic agents into the eye. The exact mechanism or reason is not known, but certainly the blood eye barrier (as analogous to the blood brain barrier) may be an important factor. On the other hand, when a drug is injected into the eye, it quickly washes out or is depleted from within the eye into the general circulation. From the therapeutic standpoint, this may be as difficult as giving no drug at all. Because of this inherent difficulty of delivering drugs into the eye, successful medical treatment of ocular diseases is totally inadequate.
The need for a solution is even more pressing in that the cause of a number of ocular diseases have now been identified and many are amenable to treatment if a proper mode of therapeutic delivery is available. It is therefore of great interest to develop modes of treatment which obviate the limitations of present modes of therapy.
There has been a substantial resistance to introduce drugs directly into one or both chambers of the eye. The many uncertainties associated with the distribution of the drug, rate of release, binding to eye components, concentration by cells, rapid loss and/or inactivation, and the like, is discouraging for the efficacy of direct introduction.